The invention relates to a noise suppressor for an electronic endoscope, and more particularly, to an apparatus which effectively suppresses noises from other instruments which may be either combined with or internally housed within an endoscope, for use with an electronic display which produces the image of an object being examined for observation in response to a video signal from a solid-state camera located within a portion of an endoscope that is adapted to be inserted into coeloma.
Recently, a rapid advance in the electronic technology has brought CCD (charge coupled device), BBD (bucket brigade device) or MOS (metal oxide semiconductor) sensors or similar solid-state camera elements into practical use, which are being increasingly utilized in electronic endoscope for observing an object being examined by an endoscope. (It is to be understood that the term "electronic endoscope" is intended to mean a combination of a mechanical endoscope of more or less common design with an associated electronic display which is used to produce an image of an affected part being observed by the endoscope.)
However, an endoscope which is provided with such electronic display may include a high frequency diathermic cutter or snare for diathermy by high frequency cautery or for sampling of a living body. In such cases, high frequency current from a power supply for diathermy may be superimposed as noise on a video signal which is obtained as a solid-state camera element is being scanned, thus causing the reproduced image on the image display to be blurred.
A high frequency current which is output from a power supply for diathermy has a frequency which is chosen above 300 kHz in order to avoid influences upon an object being examined such as human body. On the other hand, a video signal supplied to the electronic display has a frequency band of 4.3 MHz, for example, when a color picture is used. FIG. 2 graphically shows the relationship between the frequency spectrum N of a color video signal and the frequency spectrum H of a high frequency current, the spectral intensity being shown on the ordinate and the frequency being shown on the abscissa. It will be seen that the frequency spectrum H of the high frequency current has a center frequency of 0.5 MHz with a response extending to the opposite sides thereof. The spectrum H represents a band spectrum having a certain width rather than a single spectral line, which is considered to be caused by the fact that the high frequency oscillation within the power supply for diathermy includes components other than a fundamental wave, which are distorted during the amplification of a high frequency signal.
When the frequency band of the video signal for the electronic display overlaps the frequency band of a high frequency current supplied to the diathermic cutter, the electromagnetic induction between the lines which convey the video signal and the high frequency current causes the high frequency signal to be superimposed, as noise, upon the video signal, causing a blurring of an image which is reproduced on the display. In particular, when the diathermic cutter is passed through the endoscope to effect a surgical operation, the blurring of the image may prevent the object being examined from being properly recognized, and in the worst cases, require the surgical operation to be interrupted.
To eliminate such inconveniences of the prior art, noise suppressors for electronic endoscope have already been proposed (Japanese Laid-Open Patent Applications No. 69,528/1983 and No. 69,530/1983) in which a solid-state camera element and an amplifier circuit are shielded, together with a choice of the high frequency current in a frequency band which is higher than the frequency band of the video signal to avoid an interference therewith or in which the frequency band of the video signal is chosen higher than the frequency band of the high frequency current to avoid an interference therewith.
However, it will be noted that in these noise suppressors, the frequency band of either the high frequency current or the video signal must be changed, requiring a change in the specification for the power supply of diathermy or image reproducing apparatus and thus preventing the direct use of the existing power supply or image reproducing apparatus, which is inconvenient. In other words, the noise suppressor of the prior art cannot suppress the influences of a the high frequency current upon the video signal while at the same time allowing the frequency bands of the both signal components to overlap each other.
On the other hand, an endoscope is already available on the market which incorporates an ultrasonic diagnosis system having an ultrasonic probe disposed within the distal end of a portion of the endoscope which is adapted to be inserted into coeloma or having an ultrasonic mirror associated with a probe which is rotated for scanning, thus transmitting to or receiving from internal organs ultrasonic waves for depicting an acoustic picture information of such organs on an image display.
When the electronic display incorporating a solid-state camera is used in combination with such ultrasonic diagnosis system in an endoscope, the signal to or from the ultrasonic probe may be superimposed, as noise, on the video signal supplied to the electronic display, again causing a blurring of an image being reproduced.
It will be noted that a cable which transmits a signal to the ultrasonic probe or receives a signal therefrom is passed through a portion of an endoscope adapted to be inserted into coeloma from an operating end thereof for connection with the ultrasonic probe. This cable has a relatively large diameter because a high voltage on the order of several hundreds to one kilovolt peak-to-peak is supplied to the probe. If a standard cable comprising a copper wire clad with an insulating material, for example, is used, such cable does not have a sufficient durability in response to bending, and may disadvantageously cause a failure such as breakage when used in an endoscope which is subject to repeated flexure. Such inconvenience will be aggravated if the cable is shielded to suppress adverse influences upon the video signal, thereby increasing the cable diameter. Thus, there has been a need in the prior art for coaxial cable which has an increased bending resistance. The same is true with a transmission cable which supplies a high frequency current to a "Messer" located at the distal end of the endoscope when a diathermic cutter is to be used.